Water potential : This term was given by Slatyer and Taylor (1960). It is the difference in free energy or chemical potential per unit molal volume of water in a solution over its pure state at same temperature and pressure. It is denoted by Psi or Ψw and is expressed in Pascals (Pa). T
The water potential of pure water is always taken as zero at standard temperature and pressure.
Water potential (Ψw) is expressed as the sum of solute potential (Ψs) and pressure potential (Ψp).
Ψw = Ψs + Ψp
Factors affecting the water potential are as followwing:
i. Solute concentration - The dissolution of solute in water decreses its water potential. All mixtures have a water potential less than zero. More the solute more negative will be the water potential.
ii. Pressure - If pressure greater than the atmospheric pressure is aaplied to a pure water or solution, its water potential increases.